A Dt-MOS transistor is a MOS transistor having a gate electrode connected to a semiconductor layer or well region in which a channel region is formed. Thus, an input signal is applied simultaneously to the gate electrode and the semiconductor layer or the well layer in which the channel region is formed. A Dt-MOS transistor is characterized by low threshold voltage and is yet capable of realizing low OFF-current and large ON-current. Thus, a Dt-MOS transistor is thought suitable for low power consumption operation under low supply voltage. The semiconductor layer or the well region in which the channel region is formed is called “body”.